Determination of useful spectrum of a light source that is spaced apart from the measuring instrument must take account of contributions from the ultraviolet, visible, near-infrared, mid-infrared and (optionally) far-infrared, must take account of variation of these contributions with time, and must provide compensation for contributions from dark current, which would be sensed when access to the light source is interrupted. Where possible, the light sensor should use components that are already known to be reliable and robust.
What is needed is a light collimator and light intensity monitoring system that simultaneously receives and processes light in three or more overlapping or isolated wavelength intervals and estimates dark current within each interval. Preferably, the system should have a relatively small light acceptance angle, to discriminate against and prevent processing of light from a source outside a small acceptance region. Preferably, the system should permit comparison of light received in specified wavelength intervals with a dark current signal associated with each wavelength interval, for normalization purposes. Preferably, the system should maximize use of reliable, off-the-shelf components in order to maximize interchangeability and data reproducibility.